﻿#region Copyright information
// 
// Copyright © 2005-2013 Yongkee Cho. All rights reserved.
// 
// This code is a part of the Biological Object Library and governed under the terms of the
// GNU Lesser General  Public License (LGPL) version 2.1 which accompanies this distribution.
// For more information on the LGPL, please visit http://bol.codeplex.com/license.
// 
// - Filename: Chi.cs
// - Author: Yongkee Cho
// - Email: yongkeecho@gmail.com
// - Date Created: 2012-09-06 11:39 AM
// - Last Modified: 2013-01-25 3:59 PM
// 
#endregion
using System;
using System.Collections.Generic;
using System.Linq;

namespace BOL.Linq.Distances
{
    public static partial class Disimilarity
    {
        public static double Chi(this IEnumerable<double> first, IEnumerable<double> second)
        {
            var x = first.ToList();
            var y = second.ToList();
            var xMean = x.Average();
            var yMean = y.Average();
            var length = Math.Min(x.Count, y.Count);

            return Math.Sqrt(x.Zip(y, (xc, yc) => (xMean + yMean) / length / (xc + yc) * Math.Pow(xc / xMean - yc / yMean, 2)).Sum());
        }
    }
}
